Heatsink package for flip-chip IC

ABSTRACT

A semiconductor device which includes a substrate, a semiconductor element mounted on the substrate, a cap having an opening smaller than the external size of the semiconductor element for covering the semiconductor element to provide a hermetic seal, and a heatsink member mounted on the cap covering the opening and making contact with the semiconductor element via the opening. Heat generated by the semiconductor element is conducted directly to the heatsink member. A method of producing the semiconductor device includes mounting the semiconductor element onto the substrate, covering the semiconductor element with a cap which is fixed to the substrate, and mounting the heatsink member on the cap for covering the opening and making contact with the semicondutor element via the opening.

This is a continuation-in-part of U.S. application Ser. No. 076,762, nowU.S. Pat. No. 4,742,024, which is a divisional application of U.S.application Ser. No. 937,414 now U.S. Pat. No. 4,698,663 filed Dec. 3,1986.

BACKGROUND OF THE INVENTION

The present invention generally relates to semiconductor devices andmethods of producing semiconductor devices, and more particularly to asemiconductor device provided with a cap and a heatsink member and amethod of producing such a semiconductor device.

Conventionally, a semiconductor element (flip-chip) having solder bumpsor a semiconductor element having minute leads projecting to theperiphery thereof is electrically coupled face downward to a multilevelinterconnection layer (multilevel wiring layer) on a substrate and isfixed thereon. The semiconductor element is covered by a cap having theperiphery thereof soldered on the top surface of the substrate, and thesemiconductor element is hermetically sealed by the cap. A heatsink isfixed on the cap. The heat generated by the semiconductor element isconducted in a direction along the width of the cap and reaches theheatsink, and the heat is conducted within the heatsink and is radiatedfrom the surface of the heatsink.

Generally, the cap is made of Kovar (registered trademark) when thecoefficient of thermal expansion and the processing facility areconsidered. However, the thermal conductivity of Kovar is approximately20 W/m·K and is unsatisfactory. For this reason, in a semiconductordevice having the above-described construction, the cap acts as aresistance with respect to the thermal conduction and is an obstacle tothe improvement of the heat radiating efficiency.

It is possible to conceive a construction in which the heatsink ismounted directly on the semiconductor element so as to improve the heatradiating efficiency, but in this case, it is difficult to obtain aperfect hermetic seal and to miniaturize the semiconductor device as awhole.

As another example of the conventional semiconductor device, there is asemiconductor device comprising a cap made of a material having a lowthermal expansion coefficient for covering semiconductor elements. Thecap has Cu embedded portions having a high thermal conductance. Such asemiconductor device is disclosed in IBM Technical Disclosure Bulletin,Vol. 26, No. 7A, December, 1983. According to this semiconductor device,a solid column made of high thermal conductance material is located oneach semiconductor element and is in contact with the corresponding Cuembedded portion of the cap. The heat generated by the semiconductorelement is conducted via the solid column and the Cu embedded portion ofthe cap. However, according to this semiconductor device, there is aproblem in that the processes of producing the cap is complex sinceholes must be formed in the cap and the Cu embedded portions must beembedded in the holes. In addition, when the height of the semiconductorelements and the height of the solid column are inconsistent, asatisfactory contact may not be obtained between the semiconductorelement and the solid column and between the solid column and the Cuembedded portion of the cap. However, when the cap is soldered on asubstrate which has the semiconductor elements located thereon, it isvirtually impossible to check whether or not the satisfactory contactsare obtained on the inside of the cap. Furthermore, since the solidcolumn is located between the semiconductor element and the Cu embeddedportion of the cap, it is impossible to reduce the height of the cap andthe semiconductor device as a whole cannot be miniaturized.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful semiconductor device and a method of producing thesemiconductor device, in which the problems described heretofore areeliminated.

Another and more specific object of the present invention is to providea semiconductor device comprising a substrate, a semiconductor elementmounted on the substrate, a cap having an opening smaller than theexternal size of the semiconductor element for covering thesemiconductor element to provide a hermetic seal, and a heatsink membermounted on the cap to cover the opening and to make contact with thesemiconductor element via the opening. According to the semiconductordevice of the present invention, the heat radiating efficiency isimproved because the heat generated by the semiconductor element isconducted directly to the heatsink member and not via the cap. Inaddition, it is possible to obtain a satisfactory hermetic seal for thesemiconductor element because the opening in the cap is smaller than theexternal size of the semiconductor element, and the semiconductor deviceas a whole can be miniaturized because of the contact between thesemiconductor element and the heatsink member.

Still another object of the present invention is to provide a method ofproducing a semiconductor device comprising the steps of mounting asemiconductor element or a substrate, covering the semiconductor elementby a cap which is fixed to the substrate and has an opening smaller thanthe external size of the semiconductor element, and mounting a heatsinkmember on the cap to cover the opening and to make contact with thesemiconductor element via the opening. According to the method of thepresent invention, it is possible to check via the opening of the capbefore the heatsink member is mounted whether or not the cap iscorrectly fixed on the substrate.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a first embodiment of thesemiconductor device according to the present invention;

FIGS. 2, 3 and 4 are a front view, a plan view with a part of a heatsinkmember cut away, and a bottom view, respectively, showing the firstembodiment of the semiconductor device according to the presentinvention;

FIG. 5 is an enlarged view showing a left end part of the semiconductordevice shown in FIG. 1;

FIG. 6 is a disassembled view showing the semiconductor device shown inFIG. 1;

FIG. 7 is a perspective view showing a cap and a heatsink member incorrespondence with each other;

FIG. 8 is a cross sectional view showing a second embodiment of thesemiconductor device according to the present invention;

FIG. 9 is a cross-sectional view showing a third embodiment of thesemiconductor device according to the present invention;

FIGS. 10 and 11 are a cross sectional view and a front view,respectively, showing a fourth embodiment of the semiconductor deviceaccording to the present invention;

FIG. 12 is an enlarged view showing a left end part of the semiconductordevice shown in FIG. 10;

FIG. 13 is a plan view showing a fifth embodiment of the semiconductordevice according to the present invention;

FIG. 14 is a cross sectional view of the semiconductor device along aline XIX--XIX in FIG. 13;

FIG. 15 is a cross sectional view of a sixth embodiment according to thepresent invention; and

FIG. 16 is a cross sectional view of a seventh embodiment according tothe present invention.

DETAILED DESCRIPTION

First, description will be given with respect to a first embodiment ofthe semiconductor device according to the present invention, byreferring to FIGS. 1 through 7.

As shown in FIGS. 1, 2 and 6, a semiconductor device 10 generallycomprises a semiconductor element 11, a substrate 12, a cap 13, and aheatsink member 14. A plurality of minute leads 15 extend outwardly for0.7 mm, for example, from a periphery of a top face 11a of thesemiconductor element 11 as shown in FIG. 6. Circuit elements orcircuits are formed on the top face 11a, and a polyamide resin layer 16having a thickness of 50 μm to 100 μm, for example, is formed as shownin FIG. 5 as a measure against α-rays.

The semiconductor element 11 is placed face downward on a multilevelinterconnection layer (multilevel wiring layer) 17 which is formed onthe top surface of the substrate 12. That is, a bottom face 11b of thesemiconductor element 11 faces up and the top face 11a faces down, asshown in FIGS. 5 and 6. The semiconductor element 11 is electrically andmechanically coupled to the multilevel interconnection layer 17 withoutthe use of wires. As shown in FIG. 5, the multilevel interconnectionlayer 17 comprises three to four layers of wiring patterns laminated viainsulator layers made of polyamide resin and having a thickness of 10μm.

The substrate 12 is made of AlN, SiC, or Al₂ O₃ and has a thickness of0.6 mm, for example. As shown in FIGS. 1, 5 and 6, a plurality of viaholes 18 penetrate the substance 12, and a metal such as Mo and W isfilled into the via holes 18. A metallization is carried out to formsintered metal portions 19 in the via holes 18. A plurality of pins 20are provided on the bottom surface of the substrate 12 by soldering orbrazing and are fixed in correspondence with the sintered metal portions19. The leads 15 are electrically coupled to the corresponding pins 20via the corresponding sintered metal portion 19 and the multilevelinterconnection layer 17.

The pins 20 are made of Ni-plated Kovar (registered trademark),Ni-plated Be-Cu or Ni-plated W. The pins 20 have a diameter of, forexample, 0.1 mm to 0.15 mm and a length of 1.0 mm to 1.5 mm. As shown inFIG. 4, the pins 20 are arranged on the substrate 12 at portionsexcluding the central portion and the outer peripheral portion, withpitches P₁ and P₂ respectively selected to be, for example, 0.45 mm and0.90 mm.

The cap 13 is made of Kovar, for example, and has a generally invertedrectangular tray shape. The cap 13 comprises a generally rectangularraised portion 13a, a flange portion 13b and a rectangular opening 13cformed in the center of the raised portion 13a as shown in FIG. 7. Theopening 13c is smaller than the external size of the semiconductorelement 11. As shown in FIGS. 1 and 5, the flange portion 13b issoldered on the substrate 12 by a solder 21, and the portion of theraised portion 13a around the periphery of the opening 13c is fixedlysoldered on top (bottom face 11b) of the semiconductor element 11 by asolder 22. Accordingly, the semiconductor element 11 is hermeticallysealed and is packaged within a compact package. The raised portion 13aoverlaps the top of the semiconductor element 11 for a distance a of,for example, 0.5 mm. A space 23 surrounding the semiconductor element 11is filled with nitrogen or hydrogen gas, for example.

Because the cap 13 has an opening 13c, it is possible to check via theopening 13c to determine whether or not the semiconductor element 11 hasa predetermined height and the cap 13 is satisfactorily soldered on topof the semiconductor element 11. In the case where the connectionbetween the cap 13 and the semiconductor element 11 is unsatisfactory,it is possible to correct the connection by soldering via the opening13c. The size of the cap 13 can be miniaturized because the cap 13 makescontact with the top of the semiconductor element 11.

As may be seen from FIGS. 2 and 7, the heatsink member 14 has the samesize as the substrate 12. The heatsink member 14 is a rectangular platemember having a thickness of 0.8 mm, for example, and a flat steppedportion 14a is formed on the lower surface of the heatsink member 14.The stepped portion 14a has a shape corresponding to the opening 13c ofthe cap 13, and projects for a distance b from the lower surface of theheatsink member 14. The distance b is approximately equal to a thicknesst of the cap 13. The heatsink member 14 covers the cap 13 so that thestepped portion 14a fits into the opening 13c and a vertex surface 14bof the stepped portion 14a is soldered onto the bottom surface 11b ofthe semiconductor element 11 by a solder 24.

The heatsink member 14 is made of Mo, Cu, Al, AlN or SiC. The thermalconductivities of Mo, Cu, Al, AlN and SiC are 136 W/m·K, 394 W/m·K, 239W/m·K, 150-200 W/m·K and 170-270 W/m·K, respectively, and are higherthan the thermal conductivity of Kovar. In the case where the heatsinkmember 14 is made of AlN or SiC, Ni or Au is metallized on the vertexsurface 14b.

The semiconductor device 10 is connected to a printed circuit (notshown) by connecting the pins 20 to corresponding wiring patterns of theprinted circuit. For example, the printed circuit having thesemiconductor device 10 connected thereto is assembled within a computer(not shown), and a contact and cooling means (not shown) makes contactwith the top surface of the heatsink member 14.

The heat generated by the semiconductor element 11 when the computer isoperated is conducted directly to the heatsink member 14 and not via thecap 13. The heat is conducted within the heatsink member 14 and isradiated from the top surface of the heatsink member 14. In other words,the heat generated by the semiconductor element 11 is more effectivelyradiated compared to the conventional device because the cap 13 whichacts as a resistance does not exist between the semiconductor element 11and the contact and cooling means.

Next, an embodiment of the method of producing the semiconductor device10 will be described by referring to FIG. 6. First, processes ofproducing the substrate 12 will be described. The via holes 18 areformed in so-called green sheet which is essentially a ceramic sheet,and metal powder such as Mo and W powder is filled in the via holes 18.The green sheet is then baked. The metal powder inside the via holes 18is sintered, and the substrate 12 is obtained.

Then, a thin or thick conductive film is formed on the bottom surface ofthe substrate 12 to provide a pad for the pins 20. The pins 20 are thenfixed to the bottom surface of the substrate 12 by soldering or brazing.

Next, the multilevel interconnection layer 17 is formed on the topsurface of the substrate 12. Thereafter, the semiconductor element 11 ismounted on the multilevel interconnection layer 17.

Then, a preformed solder 25 having a rectangular frame shape and athickness of 50 lm to 100 lm, for example, is placed on the top surfaceof the substrate 12 under a nitrogen or hydrogen gas atmosphere, apreformed solder 26 having a thickness of 100 lm to 200 lm, for example,is placed on top of the semiconductor element 11, the cap 13 is placedon the substrate 12, the heatsink member 14 is placed on the cap 13, andthese elements are heated to, for example, 300° C. to 330° C.

Accordingly, the preformed solders 25 and 26 reflow, and the cap 13 andthe heatsink member 14 are simultaneously fixed by the soldering. At thesame time, the semiconductor element 11 is hermetically sealed by thecap 13. The preformed solder 25 includes the solder 21, and thepreformed solder 26 includes the solders 22 and 24.

The cap 13 is a pressed member and a distance h between the raisedportion 13a and the flange 13b can be accurately set. In addition, evenwhen the height of the semiconductor element 11 is inconsistent, it ispossible to check, via the opening 13c, the connection between the cap13 and the preformed solder 26 and appropriately select the thickness ofthe preformed solder 26 so as to obtain an optimum connection. For thisreason, it is possible to set the positional relationship of the cap 13,the substrate 12 and the semiconductor element 11 with a high accuracy,and the cap 13 can be soldered onto the substrate 12 and onto thesemiconductor element 11 satisfactorily.

The heatsink member 14 can be fixed on the cap 13 with ease and with ahigh accuracy because the stepped portion 14a fits into the opening 13c.Therefore, the semiconductor device 10 can be produced by simpleprocesses and is especially suited for mass production.

In the present embodiment, the semiconductor element 11, the cap 13 andthe heatsink 14 are simultaneously soldered by the preformed solder 26.However, as a modification of this method, it is possible to firstsolder the cap 13 onto the semiconductor element 11, check theconnection between the cap 13 and the semiconductor element 11 via theopening 13c, and then mounted the heatsink member 14 on the cap 13. Theconnection between the cap 13 and the semiconductor element 11 can becorrected if the connection is unsatisfactory when the checking iscarried out via the opening 13c. According to this modification, it ispossible to produce a semiconductor device which is hermetically sealedwith an extremely high reliability.

Furthermore, instead of using the semiconductor element 11, it is ofcourse possible to use a flip-chip having solder bumps.

FIGS. 8 and 9 respectively show second and third embodiments of thesemiconductor device according to the present invention. Theconstruction of semiconductor device 30 and 40, respectively, shown inFIGS. 8 and 9 are basically the same as the construction of thesemiconductor device 10 described heretofore except for the heatsinkmember. Hence, in FIGS. 8 and 9, those parts which are the same as thosecorresponding parts in FIG. 1 are designated by the same referencenumerals, and description thereof will be omitted.

In the semiconductor device 30 shown in FIG. 8, fins 31 are fixedlysoldered directly onto the semiconductor element 11 as the heatsinkmember. The semiconductor device 30 is suited for use with an air cooledsystem.

In the semiconductor device 40 shown in FIG. 9, fins 41 are fixedlysoldered directly onto the semiconductor element 11 as the heatsinkmember. The semiconductor device 40 is suited for use with a liquidcooled system, that is, immersed in a coolant such as fluorocarbon.

FIGS. 10 through 13 show a fourth embodiment of the semiconductor deviceaccording to the present invention. The construction of a semiconductordevice 50 is basically the same as the construction of the semiconductordevice 10 except for the cap. In FIGS. 10 through 13, those parts whichare the same as those corresponding parts in FIGS. 1, 2 and 5 aredesignated by the same reference numerals, and description thereof willbe omitted.

A cap 51 of the semiconductor device 50 has no flange portioncorresponding to the flange portion 13b of the semiconductor device 10described before. The portion of the cap 51 around the periphery of anopening 51a is soldered on top of the semiconductor element 11. Thelower end of a vertical wall portion 51b of the cap 51 is soldered ontothe top surface of the substrate 12. The overall size of thesemiconductor device 50 can be made more compact compared to that of thesemiconductor device 10 because the cap 51 has no flange portion.

FIGS. 13 and 14 show a fifth embodiment of the semiconductor deviceaccording to the present invention. A semiconductor device 60 differsfrom the semiconductor device 10 in that four semiconductor elements 11are mounted on a substrate 61. A cap 62 has four openings 62a incorrespondence with the four semiconductor elements 11. Each opening 62ais smaller than the external size of the corresponding semiconductorelement 11. The portions of the cap 62 around the periphery of theopenings 62a are soldered on top of the corresponding semiconductorelements 11, and a flange portion 62b of the cap 62 is soldered on thesubstrate 61. Hence, the four semiconductor elements 11 are allhermetically sealed by the cap 62.

A heatsink member 63 comprises four stepped portions 63a incorrespondence with the openings 62a. The heatsink member 63 covers thecap 62 so that each stepped portion 63a fits into the correspondingopening 62a and is soldered directly on top of the correspondingsemiconductor element 11. Accordingly, each semiconductor element 11 iscooled via the heatsink member 63 similarly as in the case of thesemiconductor device 10 described before.

FIG. 15 is a cross sectional view of a sixth embodiment of asemiconductor device according to the present invention. This embodimentdiffers from that shown in FIG. 1 in that the cap 13' has an upperportion adhering to the sides of the semiconductor element 11' placed onthe substrate 12' and a lower portion adhering to the periphery of thesubstrate 12'. The cap 13' has a step shape.

FIG. 16 is a cross sectional view of a seventh embodiment of asemiconductor device according to the present invention. This embodimentdiffers from FIG. 15 in that the cap 13" has a curve shape (i.e., isconvex shaped). The cap 13" also adheres to the side surfaces of thesemiconductor element 11'.

In both FIGS. 15 and 16 the heatsink 14' is mouned on the entire surfaceof semiconductor element 11' since the cap portions 13' and 13" do notextend onto the top surface of the semiconductor element 11', as in FIG.1, but rather only contact the side surfaces of the semiconductorelement 11'. The semiconductor device in FIGS. 15 and 16 has the furtheradvantage of forming a smaller device.

The present invention is not limited to the above-described embodiments,and various variations and modifications may be made without departingfrom the scope of the present invention.

What is claimed is:
 1. A semiconductor device comprising:a substratehaving a top surface; at least one wiring layer formed on the topsurface of said substrate; a semiconductor element having a top facemounted on the top surface of said substrate and electrically coupled tosaid wiring layer, having a bottom face and having side faces; a caphaving an external shape substantially the same size as that of saidsubstrate and a convex shape in the cross section thereof, a peripheralportion of said cap being adhered to a peripheral portion of the topsurface of said substrate and surrounding the side faces of saidsemiconductor element, said cap having a flat portion parallel to saidsubstrate at a top portion of the convex shape and having an opening inthe flat portion, which is smaller than said substrate, the openingexposing substantially the entire bottom face of said semiconductorelement; and a heatsink mounted on the flat portion of said cap and onthe exposed bottom face of said semiconductor element so as to besupported by said cap and said semiconductor element, said heatsinkhaving an external shape substantially the same size as that of saidsubstrate.